Between us, DDF and I will get you to where you'll be able to figure out how much it will take to fill any box, any time, anywhere! (This assumes you're using the American measurement system, not the metric system.)
1) Formula: Length x Width x Depth
==> make sure all are in the same unit (inches)
2) Convert to Cubic Feet: The Magic Number = 1728
(because 12 x 12 x 12 = 1728, the number of cubic inches in 1 cubic foot). Divide #1 inches by 1728.
3) That's It!
You now have the number of cubic feet
of [soil, compost] needed to fill the raised bed/swimming pool/large hole in the ground.
Just for comparison, here's the metric calculation for a raised bed like yours, filled to the same depth.
260 cm x 130 cm x 30 cm =
2.6 m x 1.3 m x 0.3 m = 1.014 m^3
Sunset Zone 17, USDA Zone 9